1. Field of the Invention
The present invention relates to an electrophotographic toner using a bioplastic and a production method thereof.
2. Description of the Related Art
In image formation according to electrophotographic mode, an electrostatically charged image is developed by a toner to be visualized. The toner image obtained by development is transferred onto paper and then fixed by heat and pressure. The above-described toner is produced by melt-kneading a mixture prepared by blending a coloring agent, a charge controlling agent and the like in a binding resin, and grinding and classifying the kneaded mixture to give prescribed particle size distribution. As the binding resin for the toner as described above, petroleum-derived resins such as styrene acrylic resins and polyester resins have been conventionally used.
Recently, there has been proposed a method in which biodegradable resins generating little load on environments in disposal and biomass plastics produced from recyclable resources are used as the toner resin, in consideration of environments. Here, biomass plastics and biodegradable plastics capable of effectively utilizing finite resources and contributing to reduction of environmental load are called a bioplastic.
Among bioplastics, polylactic acid is one of presently most promising resins. Polylactic acid is a crystalline polyester having a melting point of about 170° C., a glass transition temperature of about 60° C. and a weight-average molecular weight (Mw) of about 150000. A method where such polylactic acid is endowed with heat resistance and high durability and used in the main frame of a mobile telephone and the like has also been started to be used. When the above-described polylactic acid is used as it is as a toner resin, the grindability thereof is poor because of its hardness. In addition, because the softening temperature is high, it is unsuitable for low temperature fixity.
Japanese Patent Application Laid-Open (Kokai) Publication No. 2001-166537 discloses a technique where a toner excellent in a low temperature fixing property and having improved durability is obtained by the content ratio of a specific polylactic biodegradable resin to a terpene phenol copolymer being adjusted to 80:20 to 20:80.
Also, Japanese Patent Application Laid-Open (Kokai) Publication No. 2003-248339 discloses a technique where an excellent low temperature fixing property is attained without losing durability by blending a terpene phenol copolymer in a specific polylactic biodegradable resin in the same manner as described above, and additionally blending a prescribed amount (7% to 20%) of wax having a melting point not higher than its softening temperature.
Moreover, Japanese Patent Application Laid-Open (Kokai) Publication No. 2004-093829 discloses a technique where a low temperature fixable toner exhibiting little temporal change is obtained by containing a specific polylactic biodegradable resin and a terpene phenol copolymer and adding 1 to 3% of inorganic fine particles as the external additive.
However, it has been ascertained by studies of the inventors of the present invention that, when polylactic acids described in examples of the above-described techniques are used, high grindability cannot be accomplished easily and toner formation is difficult.
Also, Japanese Patent Application Laid-Open (Kokai) Publication No. 2012-032628 proposes a technique where the molecular weight is lowered to improve grindability by hydrolyzing polylactic acid. However, hydrolysis of polylactic acid needs a long treatment time, and therefore the workability and cost phase thereof are highly disadvantageous.